Abstract

Children with Down syndrome (DS) are at a 500-fold increased risk for developing acute myeloid leukemia (AML) before they reach five years of age. DS-AML blasts have somatic mutations in the gene encoding the essential hematopoietic transcription factor GATA-1 resulting in hypersensitivity to chemotherapeutic drugs such as cytarabine and daunorubicin. However, therapy-induced toxicity results in greater morbidity and remains a major barrier in attaining higher survival rate. Thus, alternate therapy approaches to minimize toxicity and increase efficacy are needed. Trisomy 21 and GATA-1 mutations in DS-AML are known to alter the epigenetic landscape in multiple ways. Therefore, we evaluated the efficacy of epigenetic drugs in comparison to chemotherapy in two patient-derived xenograft (PDX) models of DS-AML.

We developed two distinct PDX models by successfully engraftment and serial passage of primary DS-AML cells in NSG-B2m mice. Both PDX lines possessed GATA-1 mutation resulting in the expression of a truncated form of GATA-1. NTPL-60 had a nonsense mutation generating a premature stop codon after the initiation codon, while NTPL-386 had a 136 bp deletion in exon 2 resulting in the loss of the initiation codon. The mouse passaged cells were intravenously injected into 6-8 week old NSG-B2m mice. Once disease establishment was confirmed based on the presence of human cells in mouse peripheral blood, five mice per group were treated with vehicle or DNA methylation inhibitor azacitidine and histone deacetylase inhibitor panobinostat either singularly or in combination at a previously determined maximally tolerated dose of 2.5 mg/Kg each. NTPL-386 xenografted mice treated with azacitidine or panobinostat survived 29 and 21 days longer than the vehicle-treated mice respectively, while the mice treated with the combination survived the longest (35 days). Similarly, azacitidine and panobinostat extended the survival of mice transplanted with NTPL-60 by 48 and 31 days respectively compared to the vehicle-treated mice. NTPL-60 mice treated with the epigenetic drug combination are alive at 57 days. Thus, we observed that the azacitidine-panobinostat combination showed statistically significant (p < 0.0001) differences in leukemic burden and mouse survival compared to treatments with either drug alone in both NTPL-386 and NTPL-60 PDX models.

We also tested the efficacy of epigenetic therapy followed by chemotherapy. The inclusion of epigenetic therapy before chemotherapy prolonged survival by 39 days compared to vehicle-treated mice. Taken together, our data indicate that epigenetic therapy may be of benefit for the treatment of children with DS-AML.